1. Technical Field
The present invention relates to an electrostatic electroacoustic transducer, and in particular to an electrostatic electroacoustic transducer having an electroacoustic transducing structure of small size, low cost and high efficiency.
2. Description of the Prior Art
An electroacoustic transducer is a type of electroacoustic converters which converts electrical energy into acoustic energy through physical effects. Typically, frequencies of acoustic waves that can be heard by human ears ranges from 20 Hz to 20000 Hz. Accordingly, electroacoustic transducers, such as speakers, are typically set to perform processing within such range.
Electroacoustic transducers can be classified by various manners, such as working principles, ways of radiating, diaphragm shapes, etc. By working principles, electroacoustic transducers can be classified into, for example, electromagnetic, piezoelectric, and electrostatic electroacoustic transducers.
Currently, electromagnetic electroacoustic transducers are the most widely-used, mature and market-dominating technologies. However, electromagnetic electroacoustic transducers are difficult to be flattened due to their inherent disadvantages. This makes electromagnetic electroacoustic transducers unable to follow the tendency of product miniaturization and flattening, to meet requirements and to keep a distortion below 2-3%. Therefore, electromagnetic electroacoustic transducers have been unable to catch up with the development of speaker technologies. Piezoelectric electroacoustic transducers employs the principle that piezoelectric materials deforms when affected by an electrical field, wherein a piezoelectrically driven device is placed in an electrical field formed from audio current signals and made to displace, thereby creating a reverse voltage effect for driving the diaphragm to produce sound. Although such electroacoustic transducers are structurally flattened and miniaturized, they cannot be bent since sintering needs to be performed to the piezoelectric materials, and they have larger distortion and are more unstable than electrostatic electroacoustic transducers. Compared to electromagnetic electroacoustic transducers, electrostatic electroacoustic transducers are characterized by less distortion, simpler structure, lighter diaphragms, better resolution, and ability of capturing very slight variations in music signals. Therefore, electrostatic electroacoustic transducers are of wider applicable range and greater developing potential.
Electrostatic electroacoustic transducers employ the principle of capacitor, where a conductive diaphragm and a fixed electrode are configured to have opposite polarities so as to form a capacitor. When sound source electrical signals are applied to the two poles of such capacitor, an attraction force is produced due to the variation of the electrical field magnitude, thereby driving the diaphragm to produce sounds. Such electrostatic electroacoustic transducers is currently at the leading position, however, the insufficient efficiency thereof needs to be addressed with diaphragms of large area or application of a high audio voltage, which creates issues of electric arc, high cost and large volume. In addition, the defect of insufficient bandwidth is also one of the problems to solve.
Conventional electrostatic speakers employ one layer of diaphragm, which leads to a limited bandwidth, so it is necessary to combine multiple speakers for improvement. Besides, in order to increase efficiency, in addition to an increase in area, the driving voltage is also increased for enabling the electrical field magnitude to reach 3 kV/mm or greater, which increases the danger in using such speakers.